C2- Rates of Reactions and Energy Changes (F) Q1.

Dilute hydrochloric acid reacts with calcium carbonate to produce carbon dioxide gas.

Three different experiments were carried out using large pieces of calcium carbonate, small pieces of

calcium carbonate and powdered calcium carbonate.

The size of the calcium carbonate pieces was the only factor that was changed.

In each experiment the volume of carbon dioxide released in five minutes was measured.

The results are

Describe what this shows about the effect of the surface area of calcium carbonate on the rate of this reaction. (2) ..............................................................................................................................................

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.............................................................................................................................................. Q2.

A catalyst is added to some reactions.

Explain the meaning of catalyst. (2)

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.............................................................................................................................................. Q3. When solid ammonium chloride is added to water a colourless solution is formed.

During the process the temperature of the liquid decreases.

Describe how you would measure the change in temperature. (2)

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Q4.

When solid ammonium chloride is added to water a colourless solution is formed.

What type of chemical change causes a decrease in temperature? (1)

A combustion B endothermic C exothermic D neutralisation

(Total for question = 1 mark) Q5.

When solid ammonium chloride is added to water a colourless solution is formed.

What process has occurred? (1)

A displacement B dissolving C neutralisation D precipitation

(Total for question = 1 mark) Q6.

When solid ammonium chloride is added to water a colourless solution is formed.

In another experiment the temperature change produced in water by dissolving a different solid can be found.

Give two variables that should be kept the same in this experiment, in order to be able to compare this temperature change fairly with the temperature change produced when the ammonium chloride dissolves in water. (2)

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Q7. The apparatus shown was used by a student to investigate the reaction between strips of magnesium ribbon and excess dilute hydrochloric acid.

The word equation for the reaction is

(a) States of substances in reactions can be shown by state symbols. Explain the difference between magnesium chloride(aq) and magnesium chloride(l). (2)

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(b) Describe what you would see when magnesium ribbon reacts with dilute hydrochloric acid. (1)

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(c) Every 20 seconds, the student recorded the total volume of hydrogen produced in the reaction.

(i) Name a piece of apparatus the student should use to measure the volume of hydrogen produced. (1)

............................................................................................................................................. The results are shown on the graph.

(ii) After how many seconds had all the magnesium reacted?

(1)

........................................................... seconds (iii) The experiment is repeated using the same volume of a more concentrated hydrochloric acid solution. All other conditions were kept the same. On the graph draw a curve to show how the volume of hydrogen changes with time during this experiment.

(2) (d) A student repeated the original experiment using the same mass of magnesium as a powder instead of as ribbon. All other conditions were the same as in the first experiment.

Explain the effect on the rate of reaction of using magnesium powder instead of magnesium ribbon. (2)

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(e) When magnesium reacts with dilute hydrochloric acid there is a change in temperature.

In an experiment the results were temperature at start = 21 °C temperature at end = 62 °C Explain what conclusion can be made about the type of reaction, from these results.

(2) .............................................................................................................................................

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............................................................................................................................................. Q8.

* Hydrochloric acid reacts with magnesium metal to produce hydrogen gas. magnesium + hydrochloric acid → magnesium chloride + hydrogen

Describe how you could use magnesium ribbon and a solution of hydrochloric acid to show that decreasing the concentration of the hydrochloric acid changes the rate of this reaction.

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.............................................................................................................................................. Q9.

Energy changes and rates of reaction

(a) When zinc reacts with copper sulfate solution, zinc sulfate solution and copper are formed. (i) An experiment was carried out to measure the temperature change when zinc powder reacts with copper sulfate solution.

initial temperature of copper sulfate solution = 20 °C final temperature of mixture after the reaction = 46 °C Explain what the temperature readings show about the type of heat change that occurs during this reaction.

(2) .............................................................................................................................................

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............................................................................................................................................. (ii) Complete the equation for the reaction between zinc and copper sulfate by putting formulae in the spaces provided.

(2) Zn + CuSO4 → ..................................... + .....................................

(b) A length of magnesium ribbon was added to excess hydrochloric acid. The time for all of the magnesium to react was recorded. The experiment was repeated with the same lengths of magnesium ribbon but different concentrations of the acid. The graph shows the time taken for the magnesium to react with different concentrations of this acid.

Use the graph to explain how the rate of this reaction changes as the concentration of hydrochloric acid increases.

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*(c) Marble chips react with dilute hydrochloric acid to produce carbon dioxide gas. The rate of this reaction can be changed by changing the size of the marble chips.

Describe experiments to investigate what effect using smaller marble chips has on the rate of this reaction.

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Q10. A student investigated the rate of reaction between magnesium ribbon and excess dilute hydrochloric acid.

The word equation for the reaction is

The total volume of hydrogen evolved was measured every 10 seconds for 120 seconds.

The graph in Figure 10 shows the results obtained by the student.

Figure 10

(i) Using the graph, give the time in seconds at which the reaction stopped. (1)

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(ii) Give the reason why the reaction stopped. (1)

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(iii) Use the graph to calculate the average rate of reaction during the first 20 seconds, in cm3 of hydrogen produced per second.

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average rate of reaction = ........................................................... cm3 s–1

(iv) The experiment was repeated at a higher temperature, keeping all other conditions exactly the same. This change caused the reaction to take place more quickly. On the graph in Figure 10, sketch a line to show the results you would expect in this experiment.

(2) (v) The rate of the reaction can be changed by adding a solid catalyst to the reaction mixture.

Which line in the table shows how the final volume of hydrogen produced and the mass of the catalyst change?

(1)

(Total for question = 7 marks)

Q11. (a) A technician made some dilute sodium hydroxide solution by carefully adding some solid sodium hydroxide to pure water. This is the hazard symbol on a bottle of solid sodium hydroxide.

(i) State what this symbol shows about sodium hydroxide.

(1) .............................................................................................................................................. (ii) Sodium hydroxide solution reacts with dilute hydrochloric acid. During the reaction heat is released. What type of reaction is this?

Put a cross ( ) in the box next to your answer. (1)

A displacement B endothermic C neutralisation D precipitation

(b) A catalyst is added to some reactions. Explain the meaning of catalyst.

(2) .............................................................................................................................................. .............................................................................................................................................. ..............................................................................................................................................

(c) Dilute hydrochloric acid reacts with calcium carbonate to produce carbon dioxide gas. Three different experiments were carried out using large pieces of calcium carbonate, small pieces of calcium carbonate and powdered calcium carbonate. The size of the calcium carbonate pieces was the only factor that was changed. In each experiment the volume of carbon dioxide released in five minutes was measured. The results are

Describe what this shows about the effect of the surface area of calcium carbonate on the rate of this reaction.

(2) .............................................................................................................................................. .............................................................................................................................................. ..............................................................................................................................................

*(d) Hydrochloric acid reacts with magnesium metal to produce hydrogen gas.

magnesium + hydrochloric acid → magnesium chloride + hydrogen

Describe how you could use magnesium ribbon and a solution of hydrochloric acid to show that

decreasing the concentration of the hydrochloric acid changes the rate of this reaction.

(6)

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(Total for Question = 12 marks) Q12. * Calcium carbonate reacts with dilute hydrochloric acid to produce carbon dioxide gas.

The word equation for the reaction is

Two samples of calcium carbonate are provided. One sample is in the form of large marble chips and the other sample is in the form of small marble chips.

Describe, in detail, an investigation to find the effect of using small marble chips rather than large marble chips on the rate of this reaction.

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Mark Scheme Q1.

Answer Acceptable answers

Mark

A description to include • smaller pieces have larger surface area / ORA (1) • larger surface area, higher / faster rate (1)ORA

smaller pieces give faster rate (1) ORA allow 'bigger surface area produces more carbon dioxide' (or similarly phrased) for one mark (2)

Q2.

Answer Acceptable answers

Mark

An explanation to include • (substance that) increases rate / speeds up reaction (1) • without being used up / changed itself (1)

ignore slows down a reaction lowers activation energy reject provides energy / heat (for 2nd mark)

(2) Q3.

Q4.

Q5.

Q6.

Q7.

Q8.

Indicative Content Mark

QWC * A description / comparison/ explanation / etc including some of the following points method – what needs to be carried out • dilute the acid • (to make) different concentrations / stated concentration values • add magnesium to acid • in suitable container • equal volumes of the acids • equal lengths of magnesium observations – to make • observe/ count bubbles • highest concentration magnesium reacts, lowest concentration magnesium does not react • observe/ time magnesium disappearing • use of timer • measure volume (6)

gas produced • measure decrease in massconclusion – evidence gathered or seen • formed bubbles faster • magnesium disappears faster • gas produced faster • mass lost faster

Level 0 No rewardable content 1 1 - 2

• a limited description e.g. add magnesium to acid and time the reaction • the answer communicates ideas using simple language and uses limited scientific terminology • spelling, punctuation and grammar are used with limited accuracy

2 3 - 4 • a simple description e.g. dilute the acid, add magnesium to both acid solutions and more concentrated one bubbles faster or magnesium reacts quicker • the answer communicates ideas showing some evidence of clarity and organisation and uses scientific terminology appropriately • spelling, punctuation and grammar are used with some accuracy

3 5 - 6 • a detailed description e.g. add magnesium to different concentrations of acids in beakers: lower concentration longer time therefore slower reaction • the answer communicates ideas clearly and coherently uses a range of scientific terminology accurately • spelling, punctuation and grammar are used with few errors

Q9.

Q10.

Q11.

Answer Acceptable answers

Mark

(a)(i) corrosive damages skin / clothes causes burns (1)

(a)(ii) C neutralisation (1) (b) An explanation to

include • (substance that) increases rate / speeds up reaction (1) • without being used up / changed itself (1)

ignore slows down a reaction lowers activation energy reject provides energy / heat (for 2nd mark)

(2) (c) A description to

include • smaller pieces have larger surface area / ORA (1) • larger surface area, higher / faster rate (1)ORA

smallerpieces give fasterrate (1) ORA allow 'bigger surface area produces more carbon dioxide' (or similarly phrased) for one mark (2)

Indicative Content Mark

QWC *(d) A description / comparison/ explanation / etc including some of the following points method – what needs to be carried out • dilute the acid • (to make) different concentrations / stated concentration values • add magnesium to acid • in suitable container • equal volumes of the acids • equal lengths of magnesium observations – to make • observe/ count bubbles • highest concentration magnesium reacts, lowest concentration magnesium does not react • observe/ time magnesium disappearing • use of timer • measure volume gas produced • measure decrease in massconclusion – evidence gathered or seen • formed bubbles faster • magnesium disappears faster • gas produced faster • mass lost faster (6)

Level 0 No rewardable content 1 1 - 2

• a limited description e.g. add magnesium to acid and time the reaction • the answer communicates ideas using simple language and uses limited scientific terminology

• spelling, punctuation and grammar are used with limited accuracy

2 3 - 4 • a simple description e.g. dilute the acid, add magnesium to both acid solutions and more concentrated one bubbles faster or magnesium reacts quicker • the answer communicates ideas showing some evidence of clarity and organisation and uses scientific terminology appropriately • spelling, punctuation and grammar are used with some accuracy

3 5 - 6 • a detailed description e.g. add magnesium to different concentrations of acids in beakers: lower concentration longer time therefore slower reaction • the answer communicates ideas clearly and coherently uses a range of scientific terminology accurately • spelling, punctuation and grammar are used with few errors

Q12.